1. Field of the Invention
This invention relates to an obstacle sensing apparatus mounted on a vehicle in order to prevent accidents such as collisions. More particularly, the invention relates to an apparatus for predicting the path of travel of a vehicle and sensing obstacles present in the path of travel.
2. Description of the Related Art
As disclosed in the specification of Japanese Patent Publication No. 51-7892, for example, a known obstacle sensing apparatus of this type includes a radar unit for transmitting radar waves such as ultrasonic waves or radio waves ahead of an automotive vehicle and sensing obstacles such as vehicles located ahead, turning means for turning the radar unit in the horizontal direction, and steering angle sensing means for sensing the steering angle of the vehicle, wherein the radar unit is turned through a prescribed angle by the turning means in conformity with the steering angle sensed by the steering angle sensing means, thereby orienting the radar waves in the traveling direction of the vehicle. In recent years, an obstacle sensing apparatus for vehicles has been developed in which a scanning-type radar unit is used to scan a comparatively wide angle in the horizontal direction. During scanning, only obstacles in the region along the vehicle traveling path predicted based upon the steering angle are picked out by a microcomputer from the information obtained by scanning, whereby the detection of obstacles by the radar unit is performed while being limited to the aforesaid region by means of software.
In these types of obstacle sensing apparatus, the detection of obstacles by the radar unit is limited to the region along the vehicle traveling path by hardware or software means. In either case, when the traveling path of the vehicle is predicted, the prediction is made based upon the vehicle steering angle sensed by steering angle sensing means. This predicting method involves certain problems.
The first problem is that when a curved segment of a road such as a thruway is canted, the steering angle does not agree with the actual turning angle of the vehicle. The turning radius of the vehicle traveling path predicted based upon the steering angle is greater than the radius of curvature of the actual traveling path, namely the curved road.
The second problem is that it is normal for the driver to be constantly turning the steering wheel back and forth slightly even while the vehicle is traveling along a straight line. Consequently, when the vehicle traveling path is predicted by following up the steering angle, the path predicted will not coincide with the actual traveling path.